ICQ similar to MSN and instant messenger, but it predates them both by a long way i I remember correctly. So ICQ number is just the ID used to contact someone on it.
AIM is Alternative Investment Market, a place where companies who want public funding (like IPO (floating) on the stock market) go, but it i not as strict in its reporting requirements. Often good gains can be made investing on AIM, that's because it can be more risky too...
AIM is also probably another Instant Messaging product that I'm not familiar with.
Hope (at least some of) this helps
Chris